In order to determine how genetic information is selectively used to promote embryonic development, we are analyzing gene activity by characterizing classes within the immediate gene product hnRNAs and within the derived mRNAs, defined by the presence and absence of short and long adenylate sequences. Within each class, subsets of corresponding genes will be identified as being expressed at specific embryonic stages of the sea urchin. This identification will be achieved by screening recombinant DNA clones containing genomic DNA and cDNA sequences representing mRNAs peculiar to different embryonic stages. The structures of genes coding for poly A ion mRNAs will be compared with those coding for poly A minus mRNAs. The coordinate expression of stage-specific genes within subsets will be analyzed as a function of inherent gene structure and adjacent common sequences, possible changes in DNA sequences during development and changes in the processing of RNA transcripts. The observed increase in degree of 3' polyadenylation of both hnRNA and mRNA during development from blastula to gastrula will be examined as a possible shift in processing as well as a change in the composition of genes giving rise to the prevalent mRNAs.